Plants are known to contain resistance proteins that recognize corresponding avirulence proteins from pathogens and effect changes in the infected plant cells to restrict the spreading of the pathogens, including production of reactive oxygen species, ethylene and pathogenesis-related proteins, acceleration of lignification, and initiation of programmed cell death.
Systemic responses to trauma can be induced by a number of traumatic factors, including necrotic pathogens and wounding (by insects, wind, etc) and may be related to signals discussed in the previous paragraph produced by the resistance protein interaction with foreign proteins, as well as by responding to plant hormone signals.
In Arabidopsis thaliana, it has been proposed that one systemic resistance pathway may be regulated by salicylic acid (SA) and/or ethylene (ET). Another systemic resistance pathway may employ jasmonic acid (JA) and ethylene (ET). Both pathways require the presence of the NPR1 protein. Further details of these resistance pathways are understood as well—for instance, it has been shown that SA signals alter the redox state of NPR1 and of the transcription factor TGA1. In their reduced state, both NPR1 and TGA1 proteins localize in the nucleus, interact and lead to the expression of SA induced genes. Induced systemic resistance (ISR) is a type of resistance associated with rhizobacteria. In ISR, NPR1 also mediates the signals from the JA/ET pathway.
Compared to A. thaliana, the signal transduction pathway of defense responses in Oryza sativa (rice) is still very unclear. The endogenous SA level in rice is very high and pathogen inoculation does not increase it. However, the homolog of NPR1 has been found in rice (NH1). Overexpression of NH1 increases rice resistance toward Xanthomonas oryza pv. oryza (Xoo) and NH1 binds to members of the TGA family of transcription factors described above.
The present inventors have sought to elucidate the resistance systems in rice, and have found that a protein, designated OsGAP1 (rice GTPase activating protein-1) is elevated in resistant lines of rice when challenged by trauma and is able to confer resistance to trauma on a wide variety of plants.